The invention relates to a method of producing a tablet, in particular a detergent tablet, having at least a first and a second layer, and a product obtained thereby.
In applications involving washing agents and detergents, detergent enhancers, dishwasher detergents, disinfectants, decalcifying agents, etc., tablets have established a place for themselves on the market in recent years as a format that provides easy metering and is simple to use.
Two-layer tablets are also becoming increasingly commonplace, in which different ingredients are divided between the two layers, first as a means of separating substances that are not compatible with one another until the tablet is used, and second as a means of producing different release profiles for the substances contained in them.
These tablets are produced in presses similar to those used for single-layer tablets, although some modifications do have to be made. In the case of a two-layer tablet, a first mixture with a first composition is usually poured into a mold and subjected to a preliminary compacting process at a first pressure. Then, a second mixture having a second, different composition is poured into the mold on top of the first, pre-compacted layer, followed by a final compaction process at a second, usually higher pressure.
The problem which occurs with tablets having at least two layers is that the joint between the individual layers has to be stable enough to prevent the layers coming apart from one another during storage and transportation of the multi-layer tablets. There are numerous reasons why the layers might come apart from one another, e.g., expansion of the volume of the individual layers, reactions at the boundary surface between the layers, etc. It is therefore of crucial importance that the compositions of the individual layers are exactly aligned with one another and that the pressures applied when compressing the individual layers are accurately set. Developing and producing stable, multi-layer tablets is therefore time- and cost-intensive and is also very sensitive to any change in internal and external parameters during the process.
Accordingly, the underlying objective of the invention is to improve the known method so as to produce more stable multi-layer tablets, in which the individual layers are largely prevented from coming apart from one another.
The invention relates to a method of producing a tablet, in particular a detergent tablet, having at least a first and a second layer, comprising the following steps: (a) introducing a first metered quantity of a first particulate composition into a mold cavity of a tablet press; (b) compacting said first metered quantity at a first pressing pressure by means of a molding punch which has at least one convexity on its pressing surface to produce a first compacted layer with an indentation(s) in its top face corresponding to the convexity/convexities on the molding punch; (c) introducing a second metered quantity of a second particulate composition into the mold cavity of the tablet press on top of the first compacted layer; and (d) compacting said second metered quantity at a second pressing pressure by means of a mold punch to produce a second compacted layer with an indentation(s) in its top face. The invention also relates to a product produced by the method.
In one specific embodiment of the method proposed by the invention, steps (c) and (d), respectively, are repeated in order to produce a third and optionally additional layers.
The indentation(s) in the uppermost layer of the tablet produced by the method of the invention is (are) preferably filled. This being the case, there are several possible options, including, for example, filling with a free-flowing, curable composition, introducing and then compacting a particulate composition or introducing one or more molded pieces.
In another embodiment of the invention, if the indentation(s) in the uppermost layer of the tablet is (are) filled with molded pieces, the latter will project above the surface of-the tablet once inserted in the indentation(s). By preference, the molded piece(s) is (are) fixed in the indentation(s) by means of a substance that will produce a transport-resistant joint between tablet and molded piece, which, in a preferred embodiment, will be an adhesive.
The invention also relates to a multi-layer tablet, in particular a detergent tablet, which can be produced using the method proposed by the invention.